In 1992 Williams, working with six nongovernmental organizations (NGOs), established the International Campaign to Ban Landmines (ICBL). Williams served as founding coordinator of the group, which seeks to ban the use and deployment of antipersonnel landmines and destroy existing ones. In Oslo, Norway, in Sept. 1997, Williams and ICBL realized one of their main goals, when 89 nations signed an international treaty banning international landmines. Williams and ICBL were awarded the 1997 Nobel Peace Prize for their efforts.

Before her work with ICBL, Williams oversaw humanitarian relief projects in Central America. As deputy director of the Los Angeles–based Medical Aid for El Salvador, she organized a network of U.S. hospitals that provided free care for children wounded in the war in El Salvador. She also led fact-finding delegations to Nicaragua and Honduras. Williams cowrote After the Guns Fall Silent: The Enduring Legacy of Landmines (1995). She has master's degrees in international relations from the John Hopkins School of Advanced International Studies and in teaching Spanish and ESL from Vermont's School for International Training, and a BA from the University of Vermont.